Deciphering CD4 + T cell-mediated responses against cancer.

It's been long thought that CD8 + cytotoxic T cells play a major role in T cell-mediated antitumor responses, whereas CD4 + T cells merely provide some assistance to CD8 + T cells as the "helpers." In recent years, numerous studies support the notion that CD4 + T cells play an indispensable role in antitumor responses. Here, we summarize and discuss the current knowledge regarding the roles of CD4 + T cells in antitumor responses and immunotherapy, with a focus on the molecular and cellular mechanisms behind these observations. These new insights on CD4 + T cells may pave the way to further optimize cancer immunotherapy.